EP0725321B1

EP0725321B1 - Coated carrier particles and processes thereof

Info

Publication number: EP0725321B1
Application number: EP96300277A
Authority: EP
Inventors: John A. Creatura; Catherine A. Mcknight; Michael J. Duggan; Thomas C. Dombroski; Bernard A. Kelly; Hadi K. Mahabadi; Michael F. Cunningham
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1995-01-17
Filing date: 1996-01-15
Publication date: 2001-06-13
Anticipated expiration: 2016-01-15
Also published as: EP0725321A1; ES2158240T3; CA2164015A1; JPH08240938A; DE69613252D1; US5567562A; CA2164015C; US5518855A; JP3703550B2; BR9600094A; DE69613252T2

Description

This invention is generally directed to carrier particle compositions, and more specifically, the present invention relates to carrier particle compositions with coated carrier particles prepared by a dry powder process.
Carrier particle compositions comprised of the carrier particles of the present invention are useful in electrostatographic or electrophotographic imaging and printing systems, especially xerographic imaging processes.
Carrier particles with polymer coatings thereover and which polymers are not in close proximity in the triboelectric series are known, reference US-A-4,937,166 and US-A-4,935,326.
EP-A-011 688 describes carrier particles comprising a core coated with a resin system of tetrafluoroethylene, fluorinated polyethylene-propylene and poly(amide-imide).
Encyclopedia of Polymer Science and Technology, Vol. 5, John Wiley & Sons, USA 1966, describes the dependence of the volume resistivity of various plastics, including polyamide, on the temperature.
It is the object of the present invention to provide processes for the preparation of coated carrier particles which enable developer mixtures that are capable of generating high and useful triboelectric charging values with finely divided toner particles; and also wherein the carrier particles are of a preselected constant conductivity.
This object has been achieved with a carrier particle composition in accordance with the appended claims.
The present invention provides further the process for the preparation of coated carrier particles in accordance with the appended claims.
In embodiments of the present invention, the carrier particles are comprised of a core with coating thereover generated from a mixture of, for example, three polymers, and wherein the polymers in some embodiments are not in close proximity thereto in the triboelectric series. Moreover, in embodiments the present invention is directed to processes for the preparation of conductive carrier particles, that is with a conductivity of from 10^-14 to 10^-6 (ohm-cm)^-1, and which carriers possess stable triboelectrical characteristics in the range of from a negative 40 to a positive 40, and preferably in the range of from 20 to 25 microcoulombs per gram.
The carrier particles of the present invention are useful in imaging methods wherein relatively constant conductivity parameters are desired. Furthermore, in the aforementioned imaging processes the triboelectric charge on the carrier particles can be preselected depending on the polymer composition applied to the carrier core.
With the carriers of the present invention, which are preferably essentially completely coated, that is 100 percent coating, the conductivity is provided by the coating polymer, for example four polymers, two polymer pairs and three polymers and a number of different conductivities can be achieved in the range of, for example, 10^-6 to 10^-14 (ohm-cm)^-1; and further, with the invention carriers there is achievable in embodiments longer lifetimes, superior wear resistance, and excellent resistance to humidity as compared to the carriers of the aforementioned patents.
Moreover, when resin coated carrier particles are prepared by the powder coating process of the present invention, the majority of the coating materials are fused to the carrier surface thereby reducing the number of toner impaction sites on the carrier material. Additionally, there can be achieved with the process of the present invention, independent of one another, desirable triboelectric charging characteristics and conductivity values; that is, for example the triboelectric charging parameter is not dependent on the carrier coating weight as is believed to be the situation with the process of U.S. Patent 4,233,387 wherein an increase in coating weight on the carrier particles may function to also permit an increase in the triboelectric charging characteristics. Specifically, therefore, with the carrier compositions and process of the present invention there can be formulated developers with selected triboelectric charging characteristics and/or conductivity values in a number of different combinations.
Thus, for example, there can be formulated in accordance with the invention of the present application developers with conductivities of from 10^-14 (ohm-cm)^-1 to 10^-6 (ohm-cm)^-1 as determined in a magnetic brush conducting cell; and triboelectric charging values of from a -40 to a positive 40 microcoulombs per gram; and in embodiments a positive 10 to a positive 30 on the carrier particles as determined by the known Faraday cage technique. Thus, the developers of the present invention can be formulated with constant conductivity values with different triboelectric charging characteristics by, for example, selecting certain carrier coating mixtures.
Advantages associated with the present invention include the enablement of obtaining a range of preselected conductivities for carrier particles; permitting the preselection of the triboelectric charge desired on the carrier particles; independently varying and preselecting both conductivity and triboelectric charge; fully and completely coated cores can be obtained wherein the conductive characteristics are not primarily dependent on, or provided by the amount of coating; and long developer life exceeding, for example, 1,000,000 xerographic imaging cycles and wherein the carrier conductivity is from 10^-14 to 10^-6(ohm-cm)^-1.
The present invention enables the development of electrostatic latent images wherein the developer mixture comprises carrier particles with a coating thereover consisting of a mixture of two pairs of polymers.
Also, in another feature of the present invention there are provided positively charged toner compositions, or negatively charged toner compositions having incorporated therein carrier particles with a coating thereover comprised of a mixture of four polymers or two polymer pairs, and wherein for each polymer pair a conductive polymer is selected.
Moreover, in another feature of the present invention there are provided processes, including economical continuous processes, for the preparation of semiconductive carriers by the addition to carrier cores of a mixture of two polymers, or a conductive polymer, for example polymethylmethacrylate containing a conductive component like carbon black, and a mixture of two polymers, like KYNAR® and polymethylmethacrylate, thereby permitting the control and design of tribo and conductivity across a wide range.
Additionally, in another feature of the present invention there are provided processes for the preparation of carrier particles wherein the tribo charge and conductivity thereof can be independently controlled.
The carrier particles of the invention are comprised of a core with a coating thereover, which coating is comprised of more than two polymers and preferably four polymers. More specifically, the carrier particles selected can be prepared by mixing carrier core, or a carrier core like a low density porous magnetic, or magnetically attractable metal core carrier particles with from, for example, between 0.05 percent and 3 percent by weight, based on the weight of the coated carrier particles, with a mixture of three, or four polymers until adherence thereof to the carrier core by mechanical impaction and/or electrostatic attraction; heating the mixture of carrier core particles and polymers to a temperature, for example, of between from 93°C to 343°C and in embodiments 160°C to 343°C; for a period of time as indicated herein and in embodiments from 10 minutes to 60 minutes enabling the polymers to melt and fuse to the carrier core particles; cooling the coated carrier particles; and thereafter classifying the obtained carrier particles to a desired particle size. Examples of two polymer pairs include a first polymer pair of a conductive polymer and an insulating polymer and a second polymer pair of a conductive polymer and an insulating polymer, and wherein the polymer pairs are triboelectrically dissimilar. In embodiments, the present invention is directed to processes for the preparation of conductive carrier particles, which comprises mixing carrier core with a first polymer pair and a second polymer pair, heating the mixture, and cooling the mixture; and wherein the first and second polymer pair each contain an insulating polymer and a conductive polymer, and wherein the carrier conductivity thereof is from 10^-6 to 10^-14 (ohm-cm)^-1; a process for the preparation of carrier particles with substantially stable conductivity parameters which comprises (1) mixing carrier cores with a first polymer pair and a second polymer pair, and wherein the first and second polymer pair contains an insulating polymer and a conductive polymer; (2) dry mixing the carrier core particles and the polymer mixtures for a sufficient period of time enabling the polymer mixture to adhere to the carrier core particles; (3) heating the mixture of carrier core particles and polymer mixture to a temperature of between 93°C and 142°C (288°F), whereby the polymer mixture melts and fuses to the carrier core particles; and (4) thereafter cooling the resulting coated carrier particles; a process for the preparation of conductive carrier particles which comprises mixing a carrier core with a first polymer and a second polymer pair, heating the mixture, and cooling the mixture; and wherein the first polymer is insulating and the second polymer pair contains an insulating polymer and a conductive polymer, and wherein the carrier conductivity thereof is from 10^-6 to 10^-14 (ohm-cm)^-1; a process for the preparation of carrier particles which comprises mixing carrier cores with a first polymer pair and a second polymer pair, heating the mixture, and cooling the mixture; and wherein the first and second polymer pair each contain an insulating polymer and a conductive polymer; and a carrier composition comprised of a core with coatings comprised of a first polymer pair, or a first polymer, and a second polymer pair; and wherein the first and second polymer pair each contain an insulating polymer and a conductive polymer.
In embodiments of the present invention there are provided carrier particles comprised of a core with a coating thereover comprised of a mixture of a first dry polymer pair component and a second dry polymer pair component, and wherein the first pair is comprised of a conductive polymer like polymethylmethacrylate having dispersed therein a conductive component like carbon black and an insulating polymer like polymethylmethacrylate, and the second pair contains a conductive polymer like polyvinylidine fluoride with a conductive component like carbon black dispersed therein and an insulating polymer.
Examples of polymers selected for the first polymer pair include a first polymer pair of polymethylmethacrylate and polymethylmethacrylate with a conductive component like carbon black dispersed therein, or polystyrene and polystyrene with a conductive component like carbon black, and a second pair of polytrifluoroethyl methacrylate, or polyvinylidene fluoride, and polytrifluoroethyl methacrylate, or polyvinylidene fluoride with a conductive component dispersed therein, such as carbon black, and the like. Generally the polymer pairs each contain an insulating polymer like PMMA and a conductive polymer like PMMA with carbon black. Thus, for the two polymer pairs there can be selected PMMA, conductive PMMA, KYNAR® and conductive KYNAR® . In embodiments, there can be selected three polymers comprised of a first insulating polymer like KYNAR® , in an amount, for example, of about 20 weight percent, and a polymer pair like insulating PMMA, 70 weight percent, and about 10 weight percent of conductive PMMA, that is PMMA with a conductive component dispersed therein. Examples of polymers include those as illustrated in the patents mentioned herein such as US-A-4,937,166 and US-A-4,935,326 providing there are two polymer pairs, or three polymers present as indicated herein. The amount of polymer selected for the polymer pairs, or for the three polymer system can vary depending, for example, on the carrier characteristics desired. For example, the first polymer pair can contain an insulating polymer in an amount of from 35 to 70 weight percent and a conductive polymer in an amount of from 35 to 70 weight percent; and the second polymer pair can contain an insulating polymer in an amount of from 35 to 70 weight percent and a conductive polymer in an amount of from 35 to 70 weight percent. Moreover, examples of amounts of each polymer are as illustrated herein, such as the diagrams that follow. The first polymer pair is present, for example, in an amount of from 1 to 99 weight percent, preferably 40 to 60 weight percent and the second polymer pair is present in an amount of from 1 to 99 weight percent, preferably 60 to 40 weight percent. Examples of conductive components that can be included in the polymer coating mixtures, include carbon blacks, metals, metal oxide powders, especially tin oxide, fluorinated carbon blacks and powdered magnetites in various effective amounts such as from 1 to 50, 1 to 30, and preferably from 10 to 20 weight percent.
With further reference to the polymer coating mixture, by close proximity as used herein it is meant, for example, that the choice of the polymers selected are dictated by their position in the triboelectric series, therefore, for example, in embodiments, one may select a first polymer pair with a significantly lower triboelectric charging value than the second polymer pair. More specifically, not in close proximity refers to first and second polymer pairs that are at different electronic work function values, that is they are not at the same electronic work function value. Additionally, the difference in electronic work functions between the first and second polymer pairs is at least 0.2 electron volt, and preferably is about 2 electron volts; and moreover, it is known that the triboelectric series corresponds to the known electronic work function series for polymers, reference Electrical Properties of Polymers, Seanor, D.A., Chapter 17, Polymer Science, A.D. Jenkins, Editor, North Holland Publishing (1972).
The percentage of each polymer present in the carrier coating mixture can vary depending on the specific components selected, the coating weight and the properties desired. Generally, the coated polymer mixtures used contain from 10 to 90 percent of the first polymer pair, and from 90 to 10 percent by weight of the second polymer pair. Preferably, there are selected mixtures of polymers with from 20 to 40 percent by weight of the first polymer pair, and from 80 to 60 percent by weight of the second polymer pair.
Subsequently, developer compositions of the present invention can be generated by admixing the aforementioned carrier particles with a toner composition comprised of resin particles and pigment particles.
Various suitable solid core carrier materials, or mixtures thereof can be selected for the present invention. Characteristic core properties of importance include those that will enable the toner particles to acquire a positive charge or a negative charge, and carrier cores that will permit desirable flow properties in the developer reservoir present in the xerographic imaging apparatus. Also of value with regard to the carrier core properties are, for example, suitable magnetic characteristics that will permit magnetic brush formation in magnetic brush development processes; and also wherein the carrier cores possess desirable mechanical aging characteristics. Examples of carrier cores that can be selected include iron, steel, ferrites like copper, zinc, and manganese available from Steward Chemicals, magnetites, nickel, and mixtures thereof. Preferred carrier cores include ferrites, and sponge iron, or steel grit with an average particle size diameter of from between 30 µm (microns) to 200 µm (microns).
Also, there results, in accordance with the present invention, carrier particles of relatively constant conductivities of from between about 10^-14 (ohm-cm)^-1 to from 10^-6 (ohm-cm)^-1, for example, a 10 volt impact across a 2.54 mm gap containing carrier beads held in place by a magnet; and wherein the carrier particles are of a triboelectric charging value of from -40 microcoulombs per gram to a positive + 40 microcoulombs per gram, these parameters being dependent on the coatings selected, and the percentage of each of the polymers used as indicated hereinbefore.
Various effective suitable means can be used to apply the polymer mixture pair coatings to the surface of the carrier particles. Examples of typical means for this purpose include combining the carrier core material, and the pair mixture of polymers by cascade roll mixing, or tumbling, milling, shaking, electrostatic powder cloud spraying, fluidized bed, electrostatic disc processing, and an electrostatic curtain. Following application of the polymer mixture, heating is initiated to permit flowout of the coating material over the surface of the carrier core. The concentration of the coating material powder particles, as well as the parameters of the heating step, may be selected to enable the formation of a continuous film of the coating material on the surface of the carrier core, or permit only selected areas of the carrier core to be coated. When selected areas of the metal carrier core remain uncoated or exposed, the carrier particles will possess electrically conductive properties when the core material comprises a metal. The aforementioned conductivities can include various suitable values. Generally, however, this conductivity is from about 10^-14 to about 10^-6 (ohm-cm)^-1, as measured, for example, across a 2.54 mm magnetic brush at an applied potential of 10 volts; and wherein the coating coverage encompasses from 10 to 100 percent of the carrier core.
Illustrative examples of finely divided toner resins selected for the developer compositions of the present invention include polyamides, epoxies, polyurethanes, diolefins, vinyl resins, styrene acrylates, styrene methacrylates, styrene butadienes, polyesters such as the polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol, crosslinked polyesters.
As one toner resin there can be selected the esterification products of a dicarboxylic acid and a diol comprising a diphenol, reference US-A-3,590,000. Other preferred toner resins include styrene/methacrylate copolymers; styrene/butadiene copolymers; polyester resins obtained from the reaction of bisphenol A and propylene oxide; and branched polyester resins resulting from the reaction of dimethyl terephthalate, 1,3-butanediol, 1,2-propanediol and pentaerythritol, and reactive extruded polyesters. Generally, from 1 to 5 parts by weight of toner particles are mixed with from 10 to 300 parts by weight of the carrier particles of the present invention.
Numerous well known suitable pigments or dyes can be selected as the colorant for the toner particles including, for example, carbon black like REGAL 330® , nigrosine dye, lamp black, iron oxides, magnetites, colored magnetitites other than black, and mixtures thereof. The pigment, which is preferably carbon black, should be present in a sufficient amount to render the toner composition highly colored. Thus, the pigment particles can be present in amounts of from 3 to 20 and preferably from 5 to 15 percent by weight, based on the total weight of the toner composition, however, lesser or greater amounts of pigment particles may be selected in embodiments.
When the pigment particles are comprised of magnetites, which are a mixture of iron oxides (FeO.Fe₂O₃) including those commercially available as MAPICO BLACK", they are present in the toner composition in an amount of from 10 to 70 percent by weight, and preferably in an amount of from 20 to 50 percent by weight.
The resin particles are present in a sufficient, but effective amount, thus when 10 percent by weight of pigment, or colorant such as carbon black is contained therein, 90 percent by weight of resin material is selected. Generally, however, the toner composition is comprised of from 85 to 97 percent by weight of toner resin particles, and from 3 to 15 percent by weight of pigment particles such as carbon black.
Also encompassed within the scope of the present invention are colored toner and developer compositions comprised of toner resin particles, carrier particles, and as pigments or colorants, red, green, brown, blue, magenta, cyan and/or yellow particles, as well as mixtures thereof. These pigments are generally present in the toner composition in an amount of from 1 to 15 weight percent based on the weight of the toner resin particles.
For further enhancing the positive charging characteristics of the developer compositions described herein, and as optional components there can be incorporated into the toner or on its surface charge enhancing additives inclusive of alkyl pyridinium halides, reference US-A-4,298,672; organic sulfate or sulfonate compositions, reference US-A-4,338,390; distearyl dimethyl ammonium sulfate, bisulfates, and other similar known charge enhancing additives. Also, negative charge enhancing additives may also be selected, such as aluminum complexes, like BONTRON E-88®. These additives are usually incorporated into the toner in an amount of from 0.1 percent by weight to 20 percent by weight, and preferably from 1 to 3 percent by weight.
The toner composition of the present invention can be prepared by a number of known methods including melt blending the toner resin particles, and pigment particles or colorants followed by mechanical attrition.
Also, the toner and developer compositions of the present invention may be selected for use in electrostatographic imaging processes containing therein conventional photoreceptors, including inorganic and organic photoreceptor imaging members. Examples of imaging members are selenium, selenium alloys, and selenium or selenium alloys containing therein additives or dopants such as halogens. Furthermore, there may be selected organic photoreceptors illustrative examples of which include layered photoresponsive devices comprised of transport layers and photogenerating layers, reference US-A-4,265,990.
Images obtained with the developers composition of the present invention exhibited in embodiments acceptable solids, excellent halftones and desirable line resolution with acceptable or substantially no background deposits.
Also, there can be obtained in accordance with the process of the present invention carrier particles with positive triboelectric charging values thereon of from 10 to 80 microcoulombs per gram by, for example, selecting as carrier coatings polyethylene, and polymethylmethacrylates.
The processes and compositions of the present invention are further illustrated with reference to the following diagrams wherein PMMA is polymethylmethacrylate; CB is carbon black; PVF₂ is KYNAR® , a polyvinylidene fluoride; the Log Conductivity is for the carrier; and wherein the carrier core is iron; the tribo is for the carrier and wherein the carrier core was iron; and wherein, for example, the -13.6 on the Log diagram represents 20 percent of carbon black loaded PMMA, 40 percent of PVF₂ (KYNAR® ) and 40 percent of PMMA.
The following Examples are being supplied to further define the present invention, it being noted that these Examples are intended to illustrate and not limit the scope of the present invention. Parts and percentages are by weight unless otherwise indicated. Comparative data is also presented.

COMPARATIVE EXAMPLE I

There were prepared carrier particles by coating 2,268 grams of a Hoeganaes atomized steel core, 90 micron weight median diameter, with 22.7 grams (1 percent coating weight) of a polymer mixture comprised of 6.81 grams (30 percent) of a polyvinylidene fluoride, available as KYNAR® 301F, and 15.89 grams (70 percent) of polymethylmethacrylate, available from Soken Chemicals. These components were combined in a twin cone mixer for 20 minutes at 23.5 rpm, resulting in the polymer being uniformly distributed and mechanically and/or electrostatically attached to the carrier core. Thereafter, the resulting carrier particles were placed into a rotating tube furnace. The furnace was maintained at 204.4°C, thereby causing the polymer to melt and fuse to the core.
A developer mixture was then prepared by mixing 200 grams of the above prepared carrier with 6 grams of a toner comprised of 89 weight percent of the extruded crosslinked polyester of US-A-5,227,460, REGAL 330® carbon black, 5 weight percent, 6 weight percent of the low molecular weight wax 660P available from Sanyo Chemicals of Japan, and as a surface additive fumed silica, TS530 AEROSIL®, available from Degussa Chemicals, 1 weight percent.
Thereafter, the triboelectric charge on the carrier was determined by the known Faraday Cage process, and there were measured on the carrier 23.2 microcoulombs per gram. Further, the conductivity of the carrier as determined by forming a 2.54 mm long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 1 x 10^-14 (ohm-cm)^-1. Therefore, these carrier particles are insulating.
In all the Examples, the triboelectric charging values and the conductivity numbers were obtained in accordance with the aforementioned procedures.

EXAMPLE II

The process of Example I was repeated with a carrier coating of 65 weight percent of polymethylmethacrylate, 25 weight percent of KYNAR®, and 10 weight percent of polymethylmethacrylate with 20 percent of carbon black. The carrier tribo charge was 23.9 microcoulombs per gram, and the carrier conductivity was 3 x 10^-14 (ohm-cm)^-1.

EXAMPLE III

A developer of the present invention was prepared by repeating the processes of Example II with the exception that 4.54 grams (20 percent) of conductive polymethylmethacrylate were introduced to the polymer mixture. The polyvinylidene fluoride and polymethylmethacrylate amounts were each reduced by 10 percent providing a polymer mixture comprised of 4.54 (20 percent) grams of polyvinylidene fluoride, 13.62 grams (60 percent) of polymethylmethacrylate, and 4.54 grams (20 percent) of carbon black loaded conductive polymethylmethacrylate. The resulting carrier particles had a measured triboelectric charge thereon of 23.1 microcoulombs per gram. Also, the carrier particles had a conductivity of 6 x 10^-9 (ohm-cm)^-1, which is considered semiconductive. Therefore, by retaining the amounts of polyvinylidene fluoride and polymethylmethacrylate relatively constant and introducing 20 weight percent of carbon black loaded conductive polymethylmethacrylate, the carrier particles changed from insulative to semiconductive without affecting the triboelectric charging of the carrier particles.

EXAMPLE IV

The process of Example III was repeated with 45 weight percent of polymethylmethacrylate, 15 weight percent of KYNAR® , and 40 weight percent of carbon black loaded polymethylmethacrylate, and the conductivity of the carrier was 6 x 10^-8 (ohm-cm)^-1 and the tribo was 22.6 (microcoulombs per gram throughout).

EXAMPLE V

A developer composition of the present invention was prepared by repeating the process of Example I and further increasing the weight percent of carbon black loaded polymethylmethacrylate in the polymer mixture. The polymer mixture was comprised of 2.27 grams (10 percent) of polyvinylidene fluoride, 6.81 grams (30 percent) of polymethylmethacrylate, and 13.62 grams (60 percent) of carbon black loaded polymethylmethacrylate. There resulted on the carrier particles a triboelectric charge of 23.0 microcoulombs per gram, and the carrier particles had a conductivity of 2 x 10⁷(ohm-cm)^-1. The triboelectric charging properties of the carrier were similar to those of Example I, however, the conductivity has increased further to create a fully conductive carrier. A carrier can be considered fully conductive if the measured conductivity is of the same order of magnitude of the uncoated carrier core.

EXAMPLE VI

A developer composition of the present invention was prepared by repeating the process of Example I with the exception that the polymer mixture was comprised of 6.81 grams (30 percent) of polyvinylidene fluoride, 2.27 grams (10 percent) of polymethylmethacrylate, and 13.62 grams (60 percent) of carbon black loaded polymethylmethacrylate. There resulted on the carrier particles a triboelectric charge of 13.3 microcoulombs per gram, and the carrier particles had a conductivity of 1 x 10^-6 (ohm-cm)^-1. Thus, compared to Example II, this carrier is also semiconductive, however, the triboelectric charging properties have been altered to produce carrier particles with less triboelectric charging potential.
A carrier with a conductivity and a lower tribo than that of Example II can be formulated with 30 percent of polyvinylidene fluoride, 20 percent of polymethylmethacrylate and 50 percent of carbon black loaded conductive polymethylmethacrylate.

EXAMPLE VII

The process of Example III was repeated except that the carrier coating mixture was comprised of four polymers of 30 weight percent of PMMA, 60 weight percent of carbon black loaded conductive PMMA with 10 weight percent of carbon black dispersed therein, 5 weight percent of polytrifluoroethylmethacrylate, and 5 weight percent of conductive polytrifluoroethylmethacrylate with 10 weight percent of carbon black dispersed therein, and the carrier tribo was 23 and the carrier conductivity was 1 x 10^-9 (ohm-cm)^-1.

EXAMPLE VIII

The process of Example III was repeated except that the carrier coating mixture was comprised of four polymers of 45 weight percent of PMMA, 40 weight percent of carbon black loaded PMMA with 10 weight percent of carbon black dispersed therein, 10 weight percent of polytrifluoroethylmethacrylate, and 5 weight percent of conductive polytrifluoroethylmethacrylate with 10 weight percent of carbon black dispersed therein, and the carrier tribo was 23 and the carrier conductivity was 3 x 10^-11 (ohm-cm)^-1.

Claims

A carrier particle composition comprising a core with a coating including

a first polymer pair or a first polymer, and

a second polymer pair,

whereby the first and second polymer pair each contain an insulating polymer and a conductive polymer,

wherein the conductivity of said carrier particles is from 10^-6 to 10^-14 (ohm-cm)^-1
The carrier particle composition according to claim 1, wherein said conductive polymer has dispersed therein a conductive component and an insulating polymer.
A process for the preparation of coated carrier particles according to claim 1, comprising

mixing the carrier cores with

the first polymer pair or the first polymer, and

the second polymer pair;

heating the mixture; and

cooling the mixture.
The process in accordance with claim 3, wherein the first polymer-is insulating.
The process in accordance with claims 3 or 4, comprising

(1) dry mixing the carrier core particles and the polymer mixture for a sufficient period of time to enable the polymer mixture to adhere to the carrier core particles;

(2) heating the mixture of carrier core particles and polymer mixture to a temperature of between 93°C and 288°C, whereby the polymer mixture melts and fuses to the carrier core particles; and

(3) thereafter cooling the resulting coated carrier particles.
The process in accordance with claims 3 or 5, wherein the first and second polymer pair each contain an insulating polymer with a conductivity of about 10^-15 (ohm-cm)^-1 and a conductive polymer with a conductivity of about 10^-2 (ohm-cm)^-1.
The process in accordance with any one of claims 3, 5 or 6, wherein the first polymer pair contains an insulating polymer with a conductivity of 10^-15 (ohm-cm)^-1, and the second polymer pair contains a conductive polymer with a conductivity of 10^-2 (ohm-cm)^-1.
The process in accordance with any one of claims 3, or 5 to 7, wherein the first polymer pair is present in an amount of from 40 to 60 weight percent, and the second polymer pair is present in an amount of from 60 to 40 weight percent.
The process in accordance with any one of claims 3 to 8, wherein the coating is continuous, and is present in a thickness of from 0.2 µm (micron) to 1.5 µm (microns).